1. Field of the Invention
The present invention relates to an optical apparatus and an optical apparatus driving unit adapted for use in a television camera, a video camera system or the like, and more particularly to a zoom lens apparatus adapted for use in an ENG camera system and a driving unit therefor.
2. Related Background Art
The zoom drive control utilizing a zoom control switch or a zoom demand in an optical apparatus such as the conventional zoom lens or video lens is disclosed for example in the Japanese Patent Application Laid-open No. 51-40924.
Such zoom drive control is achieved by servo means consisting of a drive system such as a motor and a control system for controlling the function of the drive system, and a zoom control switch or a zoom demand is utilized for providing the control system of such servo means with a command signal. In the actual zooming operation, the zooming speed can be adjusted from a low speed to a high speed as desired by the operator, by the amount of manipulation of the zoom control switch or a thumb ring provided in the zoom demand.
In the image taking operation with the television camera or the video camera, there are employed various image taking techniques and various functions are proposed for realizing such image taking techniques in a simpler and exact manner.
Among such functions, there is known a position preset drive control function, in which an arbitrary zoom position is memorized in advance as a preset position, and the optical system of the zoom lens is moved to such preset position by turning on a preset zoom switch in the course of an image taking operation.
Such function will be explained with reference to FIG. 24 which is an upper external view of a zoom lens for use in an ENG camera and FIG. 25 which is a lateral external view thereof.
As shown in FIGS. 24 and 25, on a lens-barrel portion (main body portion) of the zoom lens for the ENG camera, there is mounted a lens drive unit 31 incorporating therein motors for electrical zooming, focusing and iris control, position sensors, control circuits etc.
The drive unit 31 is also provided with a zoom control switch 1 for controlling the electrical zooming, a zoom speed controlling variable resistor 3 for variably setting the drive speed of the zooming optical system in relation to the manipulation amount of the zoom control switch 1, a memory switch 8 for instructing the memory of the preset position of the zoom lens, and a preset zoom switch 7 for instructing the start of the preset operation.
In the following there will be explained the setting of the preset position and the presetting operation in the actual use of the preset function.
The setting of the preset position is executed by the operator by moving the zoom lens to a desired preset position and turning on the memory switch 8, whereby the position of the zoom lens in such state is memorized as a preset position.
Also the preset operation is executed by the operator by turning on the preset zoom switch 7, whereby the zoom lens is electrically driven to the present position. The drive speed of the zoom lens in this operation is determined by the set position of the zoom speed controlling variable resistor 3.
The above-described conventional drive unit 31 is however associated with the following drawbacks, since the drive speed of the zoom lens in the preset operation is determined by the set position of the zoom speed controlling variable resistor 3, which variably setting the drive speed of the zoom lens in relation to the manipulation amount of the zoom control switch 1.
For example in case the operator wishes to execute the zoom lens drive with the maximum speed in case of operation with the zoom control switch 1 but with a medium speed in the preset operation, it is necessary to set the zoom speed controlling variable resistor 3 at the maximum speed during the manipulation of the zoom control switch 1, then to change the setting of the zoom speed controlling variable resistor 3 to a medium speed prior to the start of the preset operation, and to set the zoom speed controlling variable resistor 3 again at the maximum speed after the preset operation is completed.
Also the operability of the zoom control switch 1 may be deteriorated if the lower limit of the setting of the zoom speed controlling variable resistor 3 is selected excessively low. For this reason, the lower limit of setting of the zoom speed controlling variable resistor 3 is inevitably limited, so that the drive speed of the zoom lens in the preset operation cannot be made very low.
On the other hand, in taking the image with the television camera or the video camera, there is known a technique of taking the image while executing zooming at a constant low speed. Such image taking technique may be utilized repeatedly in the course of image taking.
Such zooming operation has been achieved by maintaining a constant manipulation amount of the zoom control switch or the thumb ring provided in the zoom demand.
It is however not easy for the operator to maintain such constant manipulation amount of the zoom control switch or the like during the course of zooming operation. Particularly, as the zoom drive speed becomes lower, there is required a longer time for maintaining the constant manipulation amount of the zoom control switch etc., so that it is very difficult to maintain the constant manipulation amount. It is also difficult to repeatedly reproduce the same zoom drive speed.